Field of the Invention
The invention relates, in general, to a device for detecting whether obstacles are being approached during parking or turning of a motor vehicle (parking aid). In particular, the device includes a transmitting and receiving device configured in the region of at least one bumper. The transmitting and receiving device has an RF circuit configured on a printed circuit board and at least two substantially planar antennas that are connected to the RF circuit.
German Patent DE 32 44 358 C2 describes the purpose and the possible places for attaching such a parking aid to a motor vehicle (also referred to as a maneuvering aid in that document).
If the parking aid uses radio-frequency electromagnetic radiation, then the precise spatial position of the substantially planar antenna elements, also known as antenna patches, is highly important, since these patches and the patch spacing determine the directional characteristics and the radiation characteristics of the radio-frequency (RF) radiation.
The antenna patches, together with a sheet bearing them, are embedded in the plastic composition of the housing of the known parking aid. As a result, in the best-case scenario, a tolerance of .+-.0.3 mm can be achieved regarding the spacing of the antenna patch. This spacing tolerance between the RF circuit and the antenna patches leads to a disturbing variation in the acoustic warning signals emitted by the parking aid in the event that an obstacle is being approached.